1. Field of the Invention
This invention relates to a vulcanizable rubber composition comprising a partially hydrogenated unsaturated nitrile-conjugated diene copolymer.
The vulcanizable rubber composition is characterized as exhibiting a reduced heat build-up, a reduced compression set, high thermal resistance and a high mechanical strength.
2. Description of the Related Art
In recent years, there is an increasing demand for rubber parts having an enhanced thermal resistance which are set in the vicinity of an automobile engine, to cope with problems of the exhaust gas. Under this background, a partially hydrogenated unsaturated nitrile-conjugated diene copolymer rubber has been proposed and put to practical use.
The partially hydrogenated unsaturated nitrile-conjugated diene copolymer rubber is superior in ozone-resistance and thermal resistance to a conventional unsaturated nitrile-conjugated diene copolymer rubber. However, the partially hydrogenated unsaturated nitrile-conjugated diene copolymer rubber has only a reduced proportion of unsaturation and thus is difficult to vulcanize with a sulfur vulcanizer to obtain a vulcanizate having a high degree of vulcanization, and a good mechanical strength and compression set. To cope with this difficulty, proposals have been made to use a specific vulcanization promotor in combination with the vulcanizing agent.